A magnetically coupled inductive loop sensing system for less-lane disciplined traffic

A new multiple inductive loop detector system that uses the mutual inductances between an outer loop and multiple inner loops is presented in this paper. Automated detection, classification and speed measurement of vehicles are a challenging task in a no-lane and heterogeneous traffic. A recently reported multiple loop scheme is a solution but it is complex and less reliable due to large number of electrical connections required to realize the system. This paper proposes a loop sensor wherein small inner loops are placed within a large outer loop. In the new system the outer loop alone is connected to the measurement unit and all the inner loops are simply coupled inductively to the outer loop. This scheme is simple and can be easily employed to convert an existing single loop system to a multiple loop system by incorporating the inner loops. A suitable measurement scheme based on a synchronous detection is employed that guarantees accurate measurement. A special excitation that ensures parallel resonance of the whole inductive system is employed to keep the power consumption minimum. A prototype of the proposed system has been built and the practicality has been tested. The new system correctly sensed the vehicles, categorized and counted them in an undisciplined traffic.